Silk succumbs to heat processing

The silk fibroin protein that silkworms spin into cocoons is prized for its mechanical properties. But the complex network of hydrogen-bonded β-sheets that give silk its strength and flexibility also make it difficult to process with heat. Silk will burn rather than melt. To make materials from silk protein, scientists have used solution-processing methods, but these require large amounts of solvent and the silk protein tends to recrystallize in solution over time. Now, researchers led by Tufts University’s Chunmei Li and David L. Kaplan have figured out a way to turn silk protein into solid pellets that melt like plastic (Nat. Mater. 2019, DOI: 10.1038/s41563-019-0560-8). The researchers make the tiny pellets by freeze-drying an aqueous solution of silk fibroin. They then melt the pellets by heating them under pressure so that they fuse into larger pieces of material. Bulk solids made from these pellets can be machined into medical devices, like bone screws and ear tubes, that are biocompatible, biodegradable, and can be loaded with bioactive molecules, such as enzymes and drugs. Unlike silk fibroin solutions, the pellets can be stored over long periods and shipped to manufacturers.